lint: rowserrcheck

It turns out `rows.Next()` can return false on error,
avoiding error detection with `rows.Scan`

See golangci/golangci-lint#945

Fix that. In particular, `QueryRowContext` with checking for `sql.ErrNowRows`
is much simpler when expecting 0 or 1 results

Mark two false positives when only wanting schema of `LIMIT 0` query

flow/.golangci.yml

@@ -21,6 +21,7 @@ linters:
     - nonamedreturns
     - perfsprint
     - prealloc
+    - rowserrcheck
     - staticcheck
     - stylecheck
     - sqlclosecheck

flow/connectors/clickhouse/qrep.go

@@ -79,6 +79,7 @@ func (c *ClickhouseConnector) createMetadataInsertStatement(
 func (c *ClickhouseConnector) getTableSchema(tableName string) ([]*sql.ColumnType, error) {
 	//nolint:gosec
 	queryString := fmt.Sprintf(`SELECT * FROM %s LIMIT 0`, tableName)
+	//nolint:rowserrcheck
 	rows, err := c.database.Query(queryString)
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute query: %w", err)

flow/connectors/snowflake/qrep.go

@@ -82,12 +82,9 @@ func (c *SnowflakeConnector) getTableSchema(tableName string) ([]*sql.ColumnType
 	}
 
 	//nolint:gosec
-	queryString := fmt.Sprintf(`
-	SELECT *
-	FROM %s
-	LIMIT 0
-	`, snowflakeSchemaTableNormalize(schematable))
+	queryString := fmt.Sprintf("SELECT * FROM %s LIMIT 0", snowflakeSchemaTableNormalize(schematable))
 
+	//nolint:rowserrcheck
 	rows, err := c.database.QueryContext(c.ctx, queryString)
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute query: %w", err)
@@ -303,6 +300,11 @@ func (c *SnowflakeConnector) getColsFromTable(tableName string) ([]string, []str
 		colTypes = append(colTypes, colType.String)
 	}
 
+	err = rows.Err()
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to read rows: %w", err)
+	}
+
 	if len(colNames) == 0 {
 		return nil, nil, fmt.Errorf("cannot load schema: table %s.%s does not exist", schemaTable.Schema, schemaTable.Table)
 	}

flow/connectors/snowflake/snowflake.go

@@ -324,25 +324,14 @@ func (c *SnowflakeConnector) getTableSchemaForTable(tableName string) (*protos.T
 }
 
 func (c *SnowflakeConnector) GetLastOffset(jobName string) (int64, error) {
-	rows, err := c.database.QueryContext(c.ctx, fmt.Sprintf(getLastOffsetSQL,
-		c.metadataSchema, mirrorJobsTableIdentifier), jobName)
-	if err != nil {
-		return 0, fmt.Errorf("error querying Snowflake peer for last syncedID: %w", err)
-	}
-	defer func() {
-		err = rows.Close()
-		if err != nil {
-			c.logger.Error("error while closing rows for reading last offset", slog.Any("error", err))
-		}
-	}()
-
-	if !rows.Next() {
-		c.logger.Warn("No row found, returning 0")
-		return 0, nil
-	}
 	var result pgtype.Int8
-	err = rows.Scan(&result)
+	err := c.database.QueryRowContext(c.ctx, fmt.Sprintf(getLastOffsetSQL,
+		c.metadataSchema, mirrorJobsTableIdentifier), jobName).Scan(&result)
 	if err != nil {
+		if err == sql.ErrNoRows {
+			c.logger.Warn("No row found, returning 0")
+			return 0, nil
+		}
 		return 0, fmt.Errorf("error while reading result row: %w", err)
 	}
 	if result.Int64 == 0 {
@@ -362,40 +351,28 @@ func (c *SnowflakeConnector) SetLastOffset(jobName string, lastOffset int64) err
 }
 
 func (c *SnowflakeConnector) GetLastSyncBatchID(jobName string) (int64, error) {
-	rows, err := c.database.QueryContext(c.ctx, fmt.Sprintf(getLastSyncBatchID_SQL, c.metadataSchema,
-		mirrorJobsTableIdentifier), jobName)
-	if err != nil {
-		return 0, fmt.Errorf("error querying Snowflake peer for last syncBatchId: %w", err)
-	}
-	defer rows.Close()
-
 	var result pgtype.Int8
-	if !rows.Next() {
-		c.logger.Warn("No row found, returning 0")
-		return 0, nil
-	}
-	err = rows.Scan(&result)
+	err := c.database.QueryRowContext(c.ctx, fmt.Sprintf(getLastSyncBatchID_SQL, c.metadataSchema,
+		mirrorJobsTableIdentifier), jobName).Scan(&result)
 	if err != nil {
+		if err == sql.ErrNoRows {
+			c.logger.Warn("No row found, returning 0")
+			return 0, nil
+		}
 		return 0, fmt.Errorf("error while reading result row: %w", err)
 	}
 	return result.Int64, nil
 }
 
 func (c *SnowflakeConnector) GetLastNormalizeBatchID(jobName string) (int64, error) {
-	rows, err := c.database.QueryContext(c.ctx, fmt.Sprintf(getLastNormalizeBatchID_SQL, c.metadataSchema,
-		mirrorJobsTableIdentifier), jobName)
-	if err != nil {
-		return 0, fmt.Errorf("error querying Snowflake peer for last normalizeBatchId: %w", err)
-	}
-	defer rows.Close()
-
 	var normBatchID pgtype.Int8
-	if !rows.Next() {
-		c.logger.Warn("No row found, returning 0")
-		return 0, nil
-	}
-	err = rows.Scan(&normBatchID)
+	err := c.database.QueryRowContext(c.ctx, fmt.Sprintf(getLastNormalizeBatchID_SQL, c.metadataSchema,
+		mirrorJobsTableIdentifier), jobName).Scan(&normBatchID)
 	if err != nil {
+		if err == sql.ErrNoRows {
+			c.logger.Warn("No row found, returning 0")
+			return 0, nil
+		}
 		return 0, fmt.Errorf("error while reading result row: %w", err)
 	}
 	return normBatchID.Int64, nil
@@ -422,6 +399,11 @@ func (c *SnowflakeConnector) getDistinctTableNamesInBatch(flowJobName string, sy
 		}
 		destinationTableNames = append(destinationTableNames, result.String)
 	}
+
+	err = rows.Err()
+	if err != nil {
+		return nil, fmt.Errorf("failed to read rows: %w", err)
+	}
 	return destinationTableNames, nil
 }